JSFiddle - React, Tailwind, and code Playground

HTML

<div ng-app="app">
    <div ng-controller="testCtrl">
        <select ng-model="first" ng-change="selectChanged()">
            <option value="1">1</option>
            <option value="2">2</option>
        </select>
        <select ng-model="first" ng-change="selectChanged()">
            <option value="1">1</option>
            <option value="2">2</option>
        </select>
    </div>
</div>

JavaScript

angular.module('app', []).controller('testCtrl', function ($scope) {
    $scope.selectChanged = function () {
        if (angular.isDefined($scope.first) && angular.isDefined($scope.second)) {
            alert("user chose from the two drop downs.");
        }
    };
});